1. Field of the Invention
The present invention relates to an audio signal processing device with the enhancement of a low-pitch register of an audio signal by way of a missing fundamental effect.
The present application claims priority on Japanese Patent Application No. 2011-10222 filed Jan. 20, 2011, the entire content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, audio equipment manufacturers have been struggling to meet commercial needs that customers prefer to reproduce low-pitch registers of audio signals with small-size speakers, however, which cannot adequately reproduce low-pitch registers of audio signals or low-pitch registers of audio frequency. This customers' preference is common in a field of small-size audio devices and multichannel audio systems.
A multichannel audio system may be equipped with a sub-woofer (i.e. a speaker specifically used for reproduction of low-pitch sound) independently of speakers used for sound reproduction of other channels. The boundary of a low-pitch register (i.e. a crossover frequency), which is allocated to a sub-woofer among audio signals of other channels, is determined based on the performance of speakers connected to other channels. When a main channel speaker has an ability to reproduce sound above 80 Hz, for example, a low-pitch register below 80 Hz is allocated to a sub-woofer. When a main channel speaker has an ability to reproduce sound above 200 Hz, a low-pitch register below 200 Hz is allocated to a sub-woofer.
An audiovisual amplifier (i.e. an AV amplifier) with low functionality has a limited function allowing its user to set a single crossover frequency over all channels. That is, an AV amplifier should be set with a relatively high crossover frequency depending on an inexpensive speaker with a low ability of reproduction of low-pitch sound. This will be explained by taking an example in which a main speaker of a front channel is able to reproduce sound above 80 Hz while speakers of other channels (e.g. center and surround channels) are able to reproduce sound above 200 Hz. In this example, the front channel is set with a crossover frequency of 200 Hz so that a sub-woofer only may be dedicated to reproduction of sound in a low-pitch register of 80-200 Hz even through the main speaker is able to reproduce sound in the low-pitch register of 80-200 Hz.
The main speaker may demonstrate its primary performance to reproduce low-pitch sound if another speaker, such as a speaker of a center channel, has an ability to lower its reproducible frequency range.
Considering this situation, audio equipment manufacturers have been developing various types of technologies that cause a missing fundamental effect by generating harmonics, thus lowering reproducible frequencies in terms of an audio sensation by listeners.
Patent Document 1, namely Japanese Patent Application Publication No. 2010-237294, discloses an audio signal processing device that is able to reproduce sound with the enhancement of low-pitch sound by adding harmonics (belonging to the low-pitch register) to audio signals.
However, there is a problem that sound quality will be degraded since waveforms may be largely distorted by harmonics. Patent Document 1 may provide a solution to this problem, however, with a high load of processing.
Commercially available AV amplifiers with low functionality do not necessarily install high-performance digital signal processors (DSPs). These AV amplifiers are unable to achieve adequate processing on individual channels since they are unable to handle a high load of processing.
Moreover, it is difficult to adequately improve low-pitch volumes by simply adding harmonics to audio signals.